Most modern devices for multiple dose delivery of pharmaceutical substances comprise a dose setting mechanism that allows a user to selectively set a dose to be dispensed from a substance containing reservoir. Some treatment regimens require setting and administration of a dose of drug that varies over time, whereas other treatment regimens require repeated setting and administration of a fixed dose of drug. In some cases the fixed dose may need to be adjusted over time, for example during a dosage titration period.
A common type of drug delivery device is the so-called pen injector which is a pen-shaped injection device used for intermittent subcutaneous administration of an active agent. Typically, by such a pen injector the user can turn a dial about a general longitudinal axis to set a desired dose. If by accident too high a dose is set the dial may be reversed and the dose dialed down until the correct dose is reached.
This dose setting procedure requires particular attention from the user because of the importance of correct dosing. Some drugs are so potent that an overdose can be potentially lethal. However, for a person that is recommended to administer the same dose each time the above described procedure may appear somewhat undue, and it would be desirable if that person could set the particular dose each time without paying too much attention to it. Further, for people with reduced eyesight that find it difficult to read the dose scale on a drug delivery device, each dose setting is subject to a risk of eventual erroneous treatment. It would be equally desirable to provide a greater safety in the dose setting phase for this group of people.
WO 99/64092 (Owen Mumford Limited/Eli Lilly and Company) discloses a dose setting device for self-use medical injectors of the kind having a rotary dose setting knob at the rear end of a barrel that can be indexed around from a zeroed position to bring an indicator opposite a mark on a scale. The dose setting device comprises a cup-like adaptor carrying a lug and a magnifying lens. The adaptor is press fitted over the dose setting knob in a particular angular position indicating the desired dose to be set. The adaptor is rotated until the lug meets a stud on the barrel, whereby the movement is arrested and the dose has been set.
While a magnifying lens may aid the visually impaired to some degree and while the solution apparently avoids any potential excessive dialing because once the adaptor is fitted over the dose setting knob it is simply turned until it meets a physical stop, a user of this dose setting device still has to pay attention each time she/he sets a dose because the adaptor must be positioned relative to the dose setting knob in one specific angular orientation, corresponding to the desired dose, regardless of whether the specific dose is the same for each dose setting. Furthermore, with this device it is not possible to set a dose of a size that requires one, or more than one, full revolution of the dose setting knob due to the lug necessarily abutting the stud before the adaptor has been rotated 360° relative to the barrel.
WO 01/54757 (Novo Nordisk A/S) discloses a dose setting limiter for a different type of injection device in which a dose is set by turning a dial about an axis perpendicular to the general longitudinal axis of the device. The dose setting limiter comprises three parts which when arranged in particular relative angular orientations and mounted on the injection device define a pre-selected maximal allowable dose to be set. The maximal allowable dose is preselectable only when the dose setting limiter is disconnected from the injection device, and one of the three parts accordingly comprises the dose scale to allow the pre-selection.
The dose setting limiter, once in place on the injection device, may aid in securing repetitive settings of a dose that does not exceed the pre-selected maximal allowable dose. However, an adjustment of the pre-selected maximal allowable dose is either impossible, because two of the three parts are permanently fastened to one another, or cumbersome, because all three parts are disjointed and must be handled individually by the user after detachment from the injection device. Also, the injection device is in practice unusable without the dose setting limiter because the user cannot see the size of the dialed dose without the dose scale.